Air-conditioning device for vehicles, and method therefor

ABSTRACT

The invention concerns a method using a system ( 10 ) for heating or cooling air in a motor vehicle passenger compartment provided with a windscreen, by input into the passenger compartment air which has passed through an exchanger ( 12 ) comprised in a refrigerant loop. The invention is characterized in that it comprises steps which consist in measuring the temperature of the air leaving the exchanger ( 12 ), measuring the humidity of the air leaving the exchanger ( 12 ), determining the dew point of the air leaving the exchanger ( 12 ) based on said temperature and humidity, determining the windscreen temperature, comparing the dew point with the windscreen temperature and stopping the heating of air in the passenger compartment when the dew point is higher than the windscreen temperature.

The present invention relates to the technical field of air-conditioningsystems of vehicles, and more particularly to an air-conditioning systemthat ensures both cooling and heating of the air in the passengercompartment of the vehicle. The present invention also relates to amethod for use of such systems.

Air-conditioning systems are usually equipped with an external exchangerinstalled outside the passenger compartment of the vehicle, an internalexchanger installed inside the passenger compartment of the vehicle, afirst conduit via which the two exchangers are in communication and inwhich there is installed a compressor, and a second conduit via whichthe two exchangers are in communication and in which there is installeda pressure-reducing valve. The assembly formed by the two exchangers,the two lines, the compressor and the pressure-reducing valve is knownas the refrigerant loop. A refrigerant fluid is circulated therein.

An air-conditioning system of the type described in the foregoing iscapable of heating or cooling the air of the passenger compartment ofthe vehicle when it is also equipped with means for reversing thedirection of circulation of the refrigerant fluid in the refrigerantloop. The refrigerant loop then is termed reversible. In fact, when therefrigerant fluid flows via the internal exchanger, the compressor, theexternal exchanger and then the pressure-reducing valve, the internalexchanger cools the air that passes through it before being dischargedto the passenger compartment of the vehicle. Conversely, when the fluidflows via the internal exchanger, the pressure-reducing valve, theexternal exchanger and then the compressor, the air passing through theexchanger is heated before being directed toward the passengercompartment.

When the refrigerant loop is used to cool the air being sent to thepassenger compartment, the interior exchanger, which functions as anevaporator, collects water, particularly on its walls, due tocondensation of part of the humidity present in the air being treated.When the refrigerant loop reversed, operating to heat the air being sentto the passenger compartment, the internal exchanger becomes acondenser, causing rapid evaporation of the water that has accumulatedon its walls. When this air reaches the passenger compartment, it cancause extremely rapid condensation on the window surfaces of thevehicle, this phenomenon being known as “flash-fogging”, which is anuisance for the driver of the vehicle.

In one solution, there is used an air-conditioning system equipped withtwo internal heat exchangers, one dedicated to heating and the other tocooling the air of the passenger compartment.

German Patent 3907210 describes such a system, in which a first internalexchanger functions as a condenser to cool the air passing through it,and a second internal exchanger functions as an evaporator to heat theair passing through it. When the air-conditioning system is used as aheater, the first internal exchanger is idle and, conversely, when theair-conditioning system is used to cool the air of the passengercompartment, the second internal exchanger is idle.

Although the system described in German Patent 3907201 overcomes theproblem of “flash-fogging”, it requires an additional internalexchanger, which may represent a non-negligible extra cost. Furthermore,the location needed for installation of the second internal exchangermay be incompatible with the constraints of space utilization associatedwith the vehicle, especially in the motor vehicle industry.

The object of the present invention is to overcome the problem of“flash-fogging” by an air-conditioning system that is capable of bothheating and cooling the air of the passenger compartment of a vehicleand that is equipped with only a single internal exchanger.

More particularly, the invention relates to a method for use of a systemfor heating or cooling the air of a passenger compartment of a vehicleequipped with a windshield, wherein air that has passed through anexchanger belonging to a refrigerant loop is supplied to the passengercompartment, the method comprising the steps of measuring thetemperature of the air exiting the exchanger, measuring the humidity ofthe air exiting the exchanger, determining the dew point of the airexiting the exchanger from the said temperature and humidity,determining the windshield temperature, comparing the dew point with thewindshield temperature, and stopping the heating of the air in thepassenger compartment when the dew point is higher than the windshieldtemperature.

According to another characteristic of the invention, the heating of theair in the passenger compartment is stopped by diverting the air passingthrough the exchanger to the outside of the vehicle.

According to another characteristic of the invention, the air isdiverted for a specified duration, or until the dew point becomes lowerthan the windshield temperature.

According to another characteristic of the invention, the heating of theair in the passenger compartment is stopped by stopping the operation ofthe refrigerant loop.

According to another characteristic of the invention, the stoppage ofthe operation of the refrigerant loop lasts for a specified duration oris continued until the dew point is lower than the windshieldtemperature.

According to another characteristic of the invention, the operation ofthe refrigerant loop is stopped and disabled until the next restart ofthe vehicle.

Another object of the invention is to provide, for conditioning the airof the passenger compartment of a vehicle equipped with a windshield, adevice of the type comprising a first exchanger installed inside thepassenger compartment, a second exchanger installed outside thepassenger compartment, first conduits for conveying a refrigerant fluidbetween the first exchanger and the second exchanger, second conduitsfor conveying the refrigerant fluid between the first exchanger and thesecond exchanger, a compressor installed in the first conduits, apressure-reducing valve installed in the second conduits, reversingmeans for reversing the direction of circulation of the fluid in thefirst and second conduits, control means connected electrically to thecompressor, and means for evacuation of at least part of the waterpresent in the first exchanger, the said device also being equipped withfirst measuring means that transmit a signal representative of thetemperature of the air exiting the first exchanger, second measuringmeans that transmit a signal representative of the humidity of the airexiting the first exchanger, the control means being connectedelectrically to the first and second measuring means and being designedto determine the dew point of the air exiting the first exchanger fromthe signals transmitted by the first and second measuring means, todetermine the windshield temperature, to compare the said dew point andthe windshield temperature, and to activate the evacuation means whenthe dew point is higher than the windshield temperature.

According to another characteristic of the invention, the firstexchanger is installed in a main duct communicating at one end with thepassenger compartment and at a second end with the outside of thevehicle, the evacuation means comprising at least one secondary ductcommunicating at a first end with the main duct and at a second end withthe outside of the vehicle, and at least one damper designed to shut offthe secondary duct or the main duct at least partly, in alternatingmanner.

According to another characteristic of the invention, the said dampershuts off the main duct downstream from the first exchanger as definedby the direction of circulation of the air in the main duct.

Other characteristics and advantages of the invention will becomeevident by reading the description hereinafter with reference to thedrawings, wherein:

FIG. 1 schematically illustrates an air-conditioning system according toa first embodiment of the invention,

FIG. 2 illustrates the diagram of the steps of a first method for use ofa first embodiment of the device according to the invention,

FIG. 3 illustrates the diagram of the steps of a second method for useof a second embodiment of the device according to the invention,

FIG. 4 illustrates the diagram of the steps of a third method for use ofa second embodiment of the device according to the invention.

An air-conditioning system 10, illustrated in FIG. 1, intended to heator cool the air discharged into the passenger compartment (notillustrated) of a vehicle, comprises a refrigerant loop containing aninternal heat exchanger 12, which via first and second conduits 16 and17 respectively is in communication with an external heat exchanger 13.

A compressor 14, associated with reversing means 19, is installed infirst line 16, while a pressure-reducing valve 15 is installed in secondline 17. A refrigerant fluid circulates in the interior of therefrigerant loop. Reversing means 19 are capable of reversing thedirection of circulation of the refrigerant fluid in the refrigerantloop.

Internal exchanger 12 is installed in a main duct 11, which is incommunication at a first end with an air-intake port (not illustrated)opening on the outside of the vehicle, and at a second end with thepassenger compartment (if necessary via a division into a plurality ofducts). Via the air-intake port, outside air is drawn in by an impeller25 installed in main duct 11, after which it is passed through internalexchanger 12 and is finally expelled into the passenger compartment ofthe vehicle.

When the refrigerant fluid flows through external exchanger 13,pressure-reducing valve 15, internal exchanger 12 and then compressor14, interior exchanger 12 functions as an evaporator and cools the airpassing through it.

When the refrigerant fluid flows through external exchanger 13,compressor 14, internal exchanger 12 and then pressure-reducing valve15, interior exchanger 12 functions as an evaporator and heats the airpassing through it.

A control unit 20 is provided to drive reversing means 19 and thus toselect whether the mode of operation of the refrigerant loop will bethat of a heat pump or of an air cooler. Control unit 20 also drivescompressor 14 in such a way that, for example, it controls the energydelivered by internal exchanger 12 when the refrigerant loop isfunctioning as a heat pump.

Control unit 20 is connected to a first temperature sensor 22 installeddownstream from internal exchanger 12 as defined by the direction ofcirculation of air in main duct 11. First temperature sensor 22transmits to control unit 20 a signal representative of the temperatureT_(exchanger) downstream from internal exchanger 12.

Control unit 20 is connected to a humidity sensor 23 installed in theinterior of main duct 11 at a position downstream from internalexchanger 12 as defined by the direction of circulation of air in mainduct 11. Humidity sensor 23 transmits to control unit 20 a signalrepresentative of the relative humidity H_(exchanger) downstream frominternal exchanger 12.

Control unit 20 is connected to a second temperature sensor 21 installedon the outside of the vehicle. Second temperature sensor 21 transmits tocontrol unit 20 a signal representative of the temperature T_(outside)on the outside of the windshield.

Control unit 20 is further designed to determine the windshieldtemperature T_(windshield). As an example, it can receive a signalrepresentative of the windshield temperature T_(windshield) by beingdirectly connected to a third temperature sensor (not illustrated),preferably installed inside the vehicle on the windshield, or else bybeing connected to a multiplexed system with which the vehicle isequipped and on which the signal representative of the windshieldtemperature T_(windshield) is available. Nevertheless, control unit 20can calculate an estimate of the windshield temperature T_(windshield)from the signals transmitted by temperature sensor 21 for measuring theair temperature T_(outside) outside the vehicle, by a temperature sensor(not illustrated) for measuring the air temperature inside the passengercompartment, and by a vehicle-velocity sensor, according to a methodknown to those skilled in the art.

According to a first embodiment of the present invention, main duct 11is provided with condensate-evacuation means 18, comprising a secondaryduct 27, via which main duct 11 is in communication, at a positionsubstantially in the region of internal exchanger 12, with the outsideof the vehicle. A damper 26, maneuvered by actuating means 28, can bemoved into a first extreme position known as the closed position inorder to shut off the end of secondary duct 27 opening into main duct11. In a second extreme position known as the open position, damper 26is able to shut off main duct 11 at least partly, and divert the airblown by impeller 25 into secondary duct 27.

Actuating means 28 of damper 26 are driven by control unit 20.

According to a second embodiment of the device according to the presentinvention, main duct 11 is not equipped with condensate-evacuation means18, but all other elements are identical.

A first method for use of the first embodiment of the device isillustrated in FIG. 2. In step 30, the control unit receives from secondtemperature sensor 21 a signal representative of the temperatureT_(outside) outside the vehicle. In step 31, control unit 20 comparesthe value of the temperature T_(outside) outside the vehicle with athreshold temperature T_(threshold) stored in the memory of control unit20. If the temperature T_(outside) outside the vehicle is higher thanthe threshold temperature T_(threshold), a return to step 30 takesplace.

If the temperature T_(outside) outside the vehicle is lower than thethreshold temperature T_(threshold), step 32 begins, at which pointcontrol unit 20 then commands the refrigerant loop to operate as a heatpump, if necessary by driving reversing means 19 and compressor 14. Ifthe refrigerant loop is already operating as a heat pump, step 33 beginsdirectly, whereupon the control unit calculates, by a method known tothose skilled in the art, the value of the dew point T_(dewpoint)downstream from internal exchanger 12 from the temperature T_(exchanger)and humidity H_(exchanger) downstream from internal exchanger 12.

In step 34, the control unit compares the dew point T_(dewpoint) withthe windshield temperature T_(windshield), which is measured orcalculated as explained hereinabove. If the dew point T_(dewpoint) islower than the windshield temperature T_(windshield), heating of thepassenger compartment continues in step 36. If the dew pointT_(dewpoint) is higher than the windshield temperature T_(windshield),control unit 20 drives condensate-evacuation means 18 in such a way asto evacuate part of the water present on internal exchanger 12. Toaccomplish this, control unit 20 drives damper 26 to open position andmaintains damper 26 open for a specified duration. The air passingthrough moisture-laden internal exchanger 12 is evacuated to the outsideof the vehicle.

The duration for which damper 26 must be open can be determinedexperimentally so as to ensure sufficient evacuation of the waterpresent on internal exchanger 12. During this time, the control unitdrives compressor 14 in such a way that the energy released by theinternal exchanger is optimal for saturating the air passing through itwith humidity, thus permitting evacuation of the maximum quantity ofwater. In this way the duration for which damper 26 is open can beprolonged, but without exceeding a specified maximum duration, until thedew point T_(dewpoint) once again drops below the windshield temperatureT_(windshield).

The closing of damper 26 is accompanied by a return to step 30.

A second method for using the second embodiment of the device accordingto the invention, illustrated in FIG. 3, comprises steps 40, 41, 42, 43and 44, which are respectively identical to steps 30, 31, 32, 33 and 34.In step 44, control unit 20 compares the dew point T_(dewpoint) with thewindshield temperature T_(windshield). If the dew point T_(dewpoint) islower than the windshield temperature T_(windshield), the heating of thepassenger compartment is continued in step 46.

If the dew point T_(dewpoint) is higher than the windshield temperatureT_(windshield), control unit 20 drives compressor 14, in step 45, insuch a way that operation of the refrigerant loop as a heat pump isstopped. The stoppage can be prolonged for a fixed duration or else—butwithout exceeding a maximum duration—until the dew point T_(dewpoint)once again drops below the windshield temperature T_(windshield).

A third method for using the second embodiment of the device accordingto the invention, illustrated in FIG. 4, comprises 50, 51, 52, 53, 54,55 and 56, which are respectively identical to steps 40, 41, 42, 43, 44,45 and 46 of the second method for using the second embodiment of thedevice as described in the foregoing. Stoppage of the refrigerant loopin step 55 is followed by step 57, in which control unit 20 disablesoperation of the refrigerant loop as a heat pump until the vehicle isused again.

The present invention is in no way limited to the embodiment describedand illustrated, which was presented merely by way of example. To thecontrary, the invention comprises all the technical equivalents of themeans described as well as any combinations thereof that satisfy thespirit of the invention.

For example, the reversing means can be integrated with the compressor.

1. A method for use of a system for heating or cooling the air of apassenger compartment of a vehicle equipped with a windshield, whereinair that has passed through an exchanger belonging to a refrigerant loopis supplied to the passenger compartment, the method being characterizedin that it comprises the steps of measuring the temperature of the airexiting the exchanger, measuring the humidity of the air exiting theexchanger, determining the dew point of the air exiting the exchangerfrom the said temperature and humidity, determining the windshieldtemperature, comparing the dew point with the windshield temperature,and stopping the heating of the air in the passenger compartment whenthe dew point is higher than the windshield temperature.
 2. A methodaccording to claim 1, wherein the heating of the air in the passengercompartment is stopped by diverting the air passing through theexchanger to the outside of the vehicle.
 3. A method according to claim2, wherein the air is diverted for a specified duration.
 4. A methodaccording to claim 2, wherein the air is diverted until the dew pointbecomes lower than the windshield temperature.
 5. A method according toclaim 4, wherein the diversion of the air is less than a specifiedmaximum duration.
 6. A method according to claim 1, wherein the heatingof the air in the passenger compartment is stopped by stopping theoperation of the refrigerant loop.
 7. A method according to claim 6,wherein the stoppage of the operation of the refrigerant loop lasts fora specified duration.
 8. A method according to claim 6, wherein thestoppage of the operation of the refrigerant loop is continued until thedew point is lower than the windshield temperature.
 9. A methodaccording to claim 8, wherein the diversion of the air is less than aspecified maximum duration.
 10. A method according to claim 6, whereinthe operation of the refrigerant loop is stopped and disabled until thenext restart of the vehicle.
 11. A method according to claim 1, furthercomprising reversing the flow of refrigerant in said refrigerant loop.12. A device for heating or cooling the air of the passenger compartmentof a vehicle equipped with a windshield, of the type comprising a firstexchanger installed inside the passenger compartment, a second exchangerinstalled outside the passenger compartment, first conduits forconveying a refrigerant fluid between the first exchanger and the secondexchange, second conduits for conveying the refrigerant fluid betweenthe first exchanger and the second exchanger, a compressor installed inthe first conduits, a pressure-reducing valve installed in the secondconduits, reversing means for reversing the direction of circulation ofthe fluid in the first and second conduits, control means connectedelectrically to the compressor, and means for evacuation of at leastpart of the water present in the first exchanger, characterized in thatit is equipped with first measuring means that transmit a signalrepresentative of the temperature of the air exiting the firstexchanger, second measuring means that transmit a signal representativeof the humidity of the air exiting the first exchanger, the controlmeans being connected electrically to the first and second measuringmeans and being designed to determine the dew point of the air exitingthe first exchanger from the signals transmitted by the first and secondmeasuring means, to determine the windshield temperature, to compare thesaid dew point and the windshield temperature, and to activate theevacuation means when the dew point is higher than the windshieldtemperature.
 13. A device according to claim 12, wherein the firstexchanger is installed in a main duct communicating at one end with thepassenger compartment and at a second end with the outside of thevehicle, the evacuation means comprising at least one secondary ductcommunicating at a first end with the main duct and at a second end withthe outside of the vehicle, and at least one damper designed to shut offthe secondary duct or the main duct at least partly, in alternatingmanner.
 14. A device according to claim 13, wherein the said dampershuts off the main duct downstream from the first exchanger as definedby the direction of circulation of the air in the main duct.
 15. Amethod for heating or cooling air in a passenger compartment of avehicle equipped with a windshield using a reversible refrigeration loophaving a same internal exchanger for both heating and cooling the air,the method comprising the steps of: passing air through the internalexchanger; supplying the air exiting the internal exchanger to thepassenger compartment; measuring the temperature of the air exiting theinternal exchanger; measuring the humidity of the air exiting theinternal exchanger; determining a dew point of the air exiting theinternal exchanger from the measured temperature and humidity;determining the windshield temperature; comparing the dew point with thewindshield temperature; and stopping the flow of the air supplied to thepassenger compartment from the internal exchanger when the dew point ishigher than the windshield temperature.
 16. A method according to claim15, further comprising the step of stopping the flow of the air to thepassenger compartment by diverting the flow of air exiting the internalexchanger to outside of the vehicle.
 17. A method according to claim 15,wherein when the flow of the air to the passenger compartment isstopped, further comprising the step of allowing the flow of the air tothe passenger compartment when the dew point is lower than thewindshield temperature.
 18. A method according to claim 15, wherein whenthe flow of the air to the passenger compartment is stopped, furthercomprising the step of allowing the flow of the air to the passengercompartment after a set time period.
 19. A method according to claim 15,wherein when the flow of the air to the passenger compartment isstopped, further comprising the step of allowing the flow of the air tothe passenger compartment after the vehicle is shut off and restarted.